Blowout preventers are used extensively throughout the oil and gas industry. Typical blowout preventers may comprise a main body to which are attached various types of ram units. The two categories of blowout preventers that are most prevalent are ram blowout preventers and annular blowout preventers. Blowout preventer stacks frequently utilize both types, typically with at least one annular blowout preventer stacked above several ram blowout preventers. The ram units in ram blowout preventers allow for both the shearing of the drill pipe and the sealing of the blowout preventer. Typically, a blowout preventer stack may be secured to a wellhead and may provide a safe means for sealing the well in the event of a system failure.
In a typical blowout preventer, a ram bonnet assembly may be bolted to the main body using a number of high tensile bolts or studs. These bolts are required to hold the bonnet in position to enable the sealing arrangements to work effectively. Typically an elastomeric sealing element is used between the ram bonnet and the main body. There are several configurations, but essentially they are all directed to preventing a leakage bypass between the mating faces of the ram bonnet and the main body.
During normal operation, the blowout preventers may be subject to pressures up to 20,000 psi, or even higher. These high pressures often place a severe loading the retaining bolts that are used to hold the ram units in position. Consequently a large number of bolts must be employed of sufficient size to contain the force in conventional blowout preventers. Maintenance of this large number of bolts is often a cumbersome process.
The high pressures also may affect the performance of the elastomeric sealing arrangements. These elastomeric seals can degrade over time and thus require scheduled maintenance. In order to perform this maintenance, the ram bonnet must be disassembled from the main body. Because of the large numbers of bolts, the disassembly and reassembly of the blowout preventers to maintain the elastomeric sealing arrangement may also be a cumbersome process.
Furthermore, elastomer seals are reliant upon clean and damage free mating surfaces. A slight scratch or nick in the mating surfaces could render the seal ineffective, resulting in leakage.